This invention relates to a TiS.sub.2 film and a process for fabricating the same, and particularly to a flat and dense TiS.sub.2 film suitable for the cathode film of a thin film lithium secondary battery and a process for fabricating the same.
Recently, a desire for miniaturizing batteries as electric sources for electronic appliances has become keen with the miniaturization of the electronic appliances. An example of the art meeting this desire is a thin film lithium battery whose constituents, i.e. cathode, electrolyte and anode are all prepared only according to the thin film process. The thin film lithium battery has a thickness as small as about 100 .mu.m, which is considerably smaller than that of the conventional small battery usually having a thickness of about 1 mm. Furthermore, when a rechargeable thin film lithium battery can be made, a low discharge capacity, which is an inherent disadvantage of the thin film battery, can be overcome.
In fabricating a cathode film of thin film lithium battery it is necessary that its surface be flat and dense. That is, when the surface of a cathode film 2 has sharp projections 5 in forming the cathode film 2 on a substrate 1, as shown in FIG. 1, the cathode film 2 cannot be completely covered by an electrolyte film 3, and cathodes are locally exposed. Thus, when an anode film 4 is formed on the electrolyte film 3, there are short-circuits with the projections of cathode, with a failure to work as a battery.
According to studies of lithium secondary batteries so far made (for example, U.S. Pat. No. 4,203,861), it is known that TiS.sub.2 is a promising cathode material. However, the conventional batteries are prepared by bringing a cathode molding into contact of an electrolyte in a liquid state or in a pressed powder state, and no flat and dense surface is required for the cathode molding. And in fact a cathode molding in a pressed powder state with a low density and a considerable irregularity has been used.
As described above, neither a flat and dense TiS.sub.2 film applicable for a cathode film of thin film lithium battery nor a process for fabricating the same has been found yet.